The invention relates to an internal combustion engine having a carburetor and especially to an engine for a portable handheld work apparatus wherein the carburetor is connected via an intermediate piece to the engine.
In handheld work apparatus, the available space within the apparatus housing is very limited so that the individual components must be accommodated in a tight space. This concerns also the arrangement of the carburetor on the internal combustion engine so that often the carburetor is flange-connected directly to the engine block in the region of the inlet opening. However, this leads to unwanted temperature influences especially in engines having high heat generation and, for inlet openings lying high on the engine block, this leads to required forms of the housing which extend beyond the wanted housing contour. Furthermore, the extreme position of the carburetor can also lead to a poor accessibility of the adjusting screws or an unfavorable mounting of the actuating means for the starter flap and/or the carburetor flap.
To reduce the unwanted temperature influences, it has already been suggested to provide an intermediate piece having an insulating function between the engine block and the carburetor. In order to take up as little mounting space as possible, this intermediate piece has been configured in the form of a prism so that the carburetor has only a very close spacing to the engine block on the side on which the prismatic intermediate piece has its tip. For this reason, the desired insulating effect is very inadequate.
It is an object of the invention to provide an internal combustion engine with a carburetor wherein the carburetor is substantially uninfluenced by the development of heat of the engine and wherein the carburetor assumes a relative position with which the design of the housing is simplified. It is also an object of the invention to provide such an engine especially for a portable handheld work apparatus.
The internal combustion engine assembly of the invention is for a portable handheld work apparatus and includes: an internal combustion engine having an inlet opening and an engine block; a carburetor having an intake channel; a spacer for connecting the carburetor to the engine; the spacer having a channel section formed therein fluidly connecting the intake channel to the inlet opening; the spacer having a first flange lying in contact engagement with the engine block and a second flange for receiving the carburetor; the first and second flanges defining first and second flange planes, respectively, extending at least approximately parallel to each other; and, the channel section extending inclined to the flange planes.
The present invention is of special advantage in portable handheld work apparatus wherein the engine has an inlet opening very high on the engine block and, as a consequence, the carburetor would have to have an outboard or projecting housing contour. The carburetor is clearly offset in the direction of the crankcase by the spacer according to the invention and the channel running at an incline and, at the same time, an adequate spacing of the entire flange surface of the carburetor to the engine block is achieved.
A practical configuration of the spacer provides that the channel section runs along a straight line over its entire length and the longitudinal axis has the same angles to both flange surfaces. In this way, no flow deflection is required within the channel section and the angles, which are formed with respect to the contiguous components and/or the inlet openings do not operate disadvantageously on the flow of the intake air or on the flow of the mixture. The angle, which the longitudinal axis of the channel section has to the respective flanges can, for example, in each case be approximately 70xc2x0. Practically, the planes of the flanges run at least approximately parallel to the piston axis of the engine.
An air guiding plate is mounted on the spacer so that the cooling air for the engine can be maintained as a cooling air flow between the cooling ribs and so that the cooling air cannot branch off uncontrolled laterally from the engine block where it would reach the mounting region of the carburetor. The air guiding plate extends on the engine block at a spacing to the ends of the cooling ribs. This air guiding plate is advantageously planar and runs preferably in plane a parallel to the flange planes of the spacer. The air guiding plate is provided with at least one reinforcement element on the side facing away from the engine block and this reinforcement element is preferably in the form of a rib. In this way, the air guiding plate is configured so as to save as much material as possible and so that the component nonetheless has an adequate stiffness. It is practical to manufacture the spacer as one piece with the air guiding plate in order to minimize the number of individual parts and to reduce assembly costs. The spacer is preferably an injection-molded part.
In a special configuration of the invention, a pulse channel is integrated into the air guiding plate and the spacer. Such a pulse channel serves to utilize periodic pressure fluctuation for driving a gasoline pump mounted in the carburetor housing. These periodic pressure fluctuations arise in the crankcase of the engine block during operation of the engine so that the pulse channel leads from the engine block or crankcase to a membrane pump. In a practical configuration, the beginning of the pulse channel is configured as a connecting stub directed toward the engine block at an angle to the air guiding plate and the other end of the pulse channel is configured as an opening at the carburetor flange of the spacer.
In the spacer, openings are provided for fastening means or for passing fastening elements therethrough laterally next to the channel section. These openings are preferably configured as essentially cylindrical holes which extend parallel to each other and are arranged orthogonally to the flange plane. The cylindrical holes are provided, in part, for attaching the spacer to the engine block and, in part, for attaching the carburetor on the spacer. Also, these cylindrical holes start at one end of the spacer at the flange plane next to the channel section and end offset to the channel section because of the orthogonal course to the flange plane on the other side of the spacer. For this reason, the cylindrical holes lie in different planes referred to the elevation of the spacer. Insofar as the holes are provided for holding screws, these holes can be provided with insert parts which have an inner thread.
The assembly is facilitated in that all screws are screwed in orthogonally to the cylinder axis. The purger is on top and is therefore easily accessible. The intermediate piece or spacer having integrated flanges provides a space saving configuration.